1. Field of the Invention
The present invention relates to the calibration of particle emission-detecting instruments.
2. Brief Description of Related Art
In many countries regulations require that manufacturers control the amount of particulate emissions released into the environment. Emissions should be regularly monitored in order to ensure that the emissions are below the maximum levels permitted. There is a requirement that the instruments used to monitor the emissions be calibrated regularly in accordance with a standard methodology as per, for example, that of BS 3405 of the British Standards Institution.
BS 3405 is the British Standard method of measuring the concentration of particulate matter in a gas flow, e.g. emission gases in a chimney stack. The values obtained in accordance with BS 3405 are used to calibrate the instruments used to monitor particulate emissions. The method of BS 3405 involves taking a series of samples at various positions transverse of the gas flow. The series of samples is used to calculate an average mass flow rate of particulate matter through the chimney stack or other duct in question.
The sampling technique utilised in respect of BS 3405 requires the provision of isokinetic sampling equipment. The isokinetic sampling equipment should comprise sample means for isokinetically withdrawing a sample volume of the emission gas together with particulate matter associated with the sample volume. An isokinetic method of sampling ensures that the emission gas is subject to a minimum only amount of disturbance occasioned by the presence of the gas flow of the sampling means.
The measurements made according to the method of BS 3405 are claimed to be accurate only to within .+-.25%. Furthermore, the lower limit of instruments currently used to calibrate particulate emission monitoring instruments according to BS 3405 can well be above the lower levels of particulate emissions being monitored. Therefore, the method of BS 3405 is ineffective for calibrating instruments that monitor very low concentrations of particulate emissions.